In recent years, distribution of video data or audio data through the Internet is expected more and more in medium contents distribution business. A large number of standardization groups have made considerable efforts to provide a solution to the problem. One of these groups is Internet Streaming Media Alliance (ISMA). This group is working on the problem by publishing a framework for use of an interavailable existing open standard which can be used by a vender to construct an interavailable video or audio system used in an IP framework or the Internet. The specification supposes use of the existing MPEG technology and mainly focuses on the MPEG-4 technology (note that the future adoption or change may include the MPEG-2 and MPEG-7 technologies) at this time.
The ISMA or an encryption framework, i.e., ISMA Cryp for an ISMA media stream is defined. This framework can be extended to new medium and encoding, and can be upgraded for new encryption conversion, and can be used in various key management systems, a security management system, and a digital rights management (DRM) system. The framework defines encryption of a default of media streaming and certification of a medium message to the ISMA standards. FIG. 1 is a diagram showing an architecture of ISMA Crpt protection on an ISMA framework.
As is declared by the ISMA, two types of receivers are targeted. More specifically, the receivers are ISMA-only receivers and MPEG system-capable receivers. In this case, the “ISMA-only receivers” are not receivers which are compatible with an MPEG-4 system, i.e., receivers which cannot process signals in an MPEG-4 system and cannot process control (elementary) streams attachable to an arbitrary MPEG-4 (elementary) media stream. In contrast to this, the “MPEG system-capable receivers” can process MPEG-4 system layer information together with information related to the ISMA. Interavailability to the MPEG system-capable receivers can be achieved by MPEG IOD (Initial Object Description) including at least an MPEG system signal at the minimum level. The IOD is included as a binary SDP (Session Description Protocol) attribute, i.e., SDP IOD.
The ISMA Crypt can also be used in both the types of receivers. The ISMA Cryp extends binary IOD in an SDP message. New signaling (notification) provides asymmetry rather than redundancy detected in the ISMA signaling. This provides “minimum” and “basic” notification parameters of the SDP IOD to maximize the interavailability to MPEG-4 IPMP systems of the receivers.
However, current ISMA Cryp extended and defined for the IOD is not perfect and is not matched with the latest MPEG-4 IPMP extension standards. As a result, the ISMA stream may not correctly recognized by an MPEG-4 IPMP extension compatible receiver. For example, the ISMA Cryp standards define that the presence of an IPMP_Descriptor in the IOD is used to show ISMA Cryp protection. However, according to the MPEG-4 IPMP extension, a tool list descriptor must be present in the IOD when the IPMP protection is established. These match and mismatch may spoil the interavailability of the ISMA framework to the MPEG-4 IPMP extension compatible receiver.